Deterioration Rate Determination Method of Lambda Sensor and System Thereof

ABSTRACT

A degradation rate decision method of a lambda sensor, may include an injection step injecting a reducing agent so as to regenerate a nitrogen oxide purification catalyst, a lambda value detection step detecting a lambda value of the lambda sensor from a fuel/air ratio of exhaust gas after injecting the reducing agent, a reaching time decision step determining a time period that the lambda value takes to reach a predetermined criterion value after injecting the reducing agent, and a degradation rate decision step determining that the lambda sensor is degraded when the time period is equal to or longer than a predetermined time period.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No. 10-2009-0119357 filed in the Korean Intellectual Property Office on Dec. 3, 2009, the entire contents of which is incorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a degradation rate determination method of a lambda sensor and a system thereof. More particularly, the present invention relates to a degradation rate determination method of a lambda sensor and a system thereof in which a nitrogen oxide catalyst is provided to trap and purify a nitrogen oxide, and the degradation rate of the lambda sensor detecting the concentration of a reducing agent is detected so as to regenerate the nitrogen oxide catalyst.

2. Description of Related Art

Generally, exhaust gas that is exhausted through an exhaust manifold of an engine is induced to pass through a catalytic converter that is mounted in the middle of an exhaust pipe to be purified, and noise thereof is reduced while passing through a muffler before the exhaust gas is discharged to the outside through a tail pipe.

The purification catalyst processes pollution materials that are included in the exhaust gas. Further, a particulate filter is mounted on the exhaust pipe to trap particulate material (PM) that is included in the exhaust gas.

Further, a nitrogen oxide purification catalyst is prepared so as to reduce the nitrogen oxide included in the exhaust gas. A reducing agent is injected so as to regenerate the nitrogen oxide purification catalyst, and a lambda sensor is mounted to detect the concentration of the reducing agent as oxygen concentration.

A lambda value detected by the lambda sensor is used in real time to detect a rich condition of the reducing agent, and a technique using the detected lambda value to determine the regeneration condition of the nitrogen oxide purification catalyst has been being developed.

However, there is a problem that a control flow is not performed accurately and quickly by a defect and degradation of the lambda sensor.

The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

BRIEF SUMMARY OF THE INVENTION

Various aspects of the present invention are directed to provide a degradation rate determination method of a lambda sensor and the system thereof having advantages of detecting a real time degradation rate and trouble of a lambda sensor.

In an aspect of the present invention, the degradation rate decision method of a lambda sensor may include an injection step injecting a reducing agent so as to regenerate a nitrogen oxide purification catalyst, a lambda value detection step detecting a lambda value of the lambda sensor from an oxygen concentration value or a reducing agent concentration value of exhaust gas after injecting the reducing agent, a reaching time decision step determining a time period that the lambda value takes to reach a predetermined criterion value after injecting the reducing agent, and a degradation rate decision step determining that the lambda sensor is degraded when the time period is equal to or longer than a predetermined time period.

The criterion value may be selected from stored map data.

A degradation rate decision system of a lambda sensor may include a nitrogen oxide purification catalyst trapping nitrogen oxide included in an exhaust gas flowing in an exhaust line, the lambda sensor mounted on the exhaust line to detect a lambda value as a concentration of a reducing agent included in the exhaust gas, an injector that is mounted at an upstream side of the nitrogen oxide purification catalyst to inject the reducing agent, and a control portion detecting regeneration timing of the nitrogen oxide purification catalyst and controlling the injector to inject the reducing agent, wherein the control portion includes a set of instructions to perform methods as aforementioned.

The lambda sensor may include a front lambda sensor disposed at an upstream side of the nitrogen oxide purification catalyst, and a rear lambda sensor disposed at a downstream side of the nitrogen oxide purification catalyst.

The injector may inject fuel at an upstream side of the front lambda sensor.

The control portion may firstly detect the degradation rate of the front lambda sensor, and may secondly detect the degradation rate of the rear lambda sensor.

The control portion may determine that the regeneration of the nitrogen oxide purification catalyst is finished at a dropping time of the lambda value, after the lambda value of the rear lambda sensor reaches a predetermined criterion value in a predetermined time period measured from a time that the reducing agent is injected.

According to the present invention as stated above, fuel as a reducing agent is injected so as to regenerate a nitrogen oxide purification catalyst, and the degradation rate of the lambda sensor is easily detected in real time by detecting the concentration of the reducing agent.

The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description of the Invention, which together serve to explain certain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a degradation rate decision system of a lambda sensor according to an exemplary embodiment of the present invention.

FIG. 2 is a flowchart showing a degradation rate decision method of a lambda sensor according to an exemplary embodiment of the present invention.

FIG. 3 is a graph showing a lambda value detected by a lambda sensor with regard to time according to an exemplary embodiment of the present invention.

It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.

FIG. 1 is a schematic diagram showing a degradation rate decision system of a lambda sensor according to an exemplary embodiment of the present invention.

Referring to FIG. 1, an exhaust system includes a nitrogen oxide purification catalyst 130 mounted in an exhaust line, a front lambda sensor 110 mounted at an upstream side of the nitrogen oxide purification catalyst 130, a rear lambda sensor 120 mounted at a downstream side of the nitrogen oxide purification catalyst 130, and an injector 140 injecting a reducing agent into the exhaust line, wherein the front lambda sensor 110, the rear lambda sensor 120, the nitrogen oxide purification catalyst 130, and the injector 140 are electrically connected to a control portion 100.

In an exemplary embodiment of the present invention, the injector 140, the front lambda sensor 110, the nitrogen oxide purification catalyst 130, and the rear lambda sensor 120 are sequentially disposed along the exhaust line.

The control portion 100 determines regeneration timing of the nitrogen oxide purification catalyst 130 and controls the injector to inject the reducing agent. In the exemplary embodiment of the present invention, the reducing atmosphere is made by the injector 140 injecting the fuel, and can be created by a post injection of the fuel according to operating condition of the engine.

Further, the front lambda sensor 110 and the rear lambda sensor 120 detect a lambda value as a concentration of oxygen, and transfer the signal thereof to the control portion 100.

That is, if the lambda value detected by the front lambda sensor 110 or the rear lambda sensor 120 is large, the concentration of the reducing agent within the exhaust gas is lean and the amount of oxygen is relatively high, and if the lambda value is small, the concentration of the reducing agent is rich and the amount of oxygen is relatively low.

The nitrogen oxide purification catalyst 130 traps nitrogen oxide in a condition in which the fuel component as the reducing agent of the exhaust gas flowing in the exhaust line is lean, and reduces the trapped nitrogen oxide to nitrogen, oxygen, and water.

That is, the nitrogen oxide purification catalyst 130 oxidizes nitrogen monoxide to nitrogen dioxide, and the nitrogen dioxide reacts with catalyst components (barium oxide) to be trapped within the nitrogen oxide purification catalyst 130 in a trapping mode.

Further, the nitrogen dioxide is transformed to nitrogen and water and the nitrogen monoxide is transformed to nitrogen and carbon dioxide through carbon monoxide, hydrogen, and hydrocarbon as the reducing agent in a regeneration mode. In this case, the catalyst components included in the nitrogen oxide purification catalyst include platinum or barium.

A method for determining the regeneration timing of the nitrogen oxide purification catalyst 130 and the structure of the exhaust system are known to the public, so detailed descriptions thereof are omitted in an exemplary embodiment of the present invention.

FIG. 2 is a flowchart showing a degradation rate decision method of a lambda sensor according to an exemplary embodiment of the present invention.

Referring to FIG. 2, a method for detecting degradation rate of the lambda sensor includes a zero step S200, a first step S210, a second step S220, a third step S230, a third step S230, a fourth step S240, a fifth step S250, a sixth step S260, a seventh step S270, and an eighth step S280.

The zero step S200 starts a rich mode. The fuel as the reducing agent is injected by the injector 140 so as to perform the zero step S200, such that the concentration of the reducing agent included in the exhaust gas becomes rich and the oxygen concentration becomes lean.

Time is counted after injecting the reducing agent through the injector 140 in the first step S210.

Further, a lambda value indicating the concentration of the reducing agent is detected by the oxygen concentration detected by the front lambda sensor 110, and the detected lambda value is compared with a rich criterion value in the second step S220. In this case, the rich criterion value is a predetermined value determining whether the reducing agent is rich or not.

The time that the lambda value detected by the front lambda sensor 110 takes to reach the rich criterion value is detected in the seventh step S270, and it is determined whether the reaching time is longer than a predetermined time.

If the reaching time is longer than a predetermined time, it is determined that the front lambda sensor 110 is degraded in the eighth step S280, and if the reaching time is shorter than that, it is determined that the front lambda sensor 110 is in a normal condition in the ninth step S290.

The time that the rear lambda sensor 120 takes to reach a rich criterion value in the third step S230 is detected, and it is determined whether the reaching time is longer than a predetermined time.

If the reaching time is longer than a predetermined time, it is determined that the rear lambda sensor 120 is degraded in the fifth step, and if the reaching time is shorter than that, it is determined that the rear lambda sensor 120 is in a normal condition in the sixth step S260.

It is desirable that the degradation rate of the front lambda sensor 110 is detected earlier than the rear lambda sensor 120 in an exemplary embodiment of the present invention.

Since the reducing agent injected by the injector 140 first passes through the front lambda sensor 100, the front lambda sensor 110 reacts with the reducing agent sooner than the rear lambda sensor 120.

FIG. 3 is a graph showing a lambda value detected by a lambda sensor with regard to time according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the horizontal axis represents time, and the vertical axis represents lambda value.

The lambda value represents the concentration (rich or lean) of oxygen included in the exhaust gas, and if the value is high, the concentration of the reducing agent in the exhaust gas is in a lean condition, if the value is low, the concentration of the reducing agent in the exhaust gas is in a rich condition.

A criterion value of a rich condition is 1, and if the lambda value is smaller than 1, the reducing agent concentration is rich, while if the lambda value is larger than 1, the reducing agent concentration is lean.

As shown, if the regeneration is started by injecting the reducing agent through the injector 140, the lambda value of the front lambda sensor 110 descends, passes the rich criterion value of 1, and reaches a lambda value of 0.92.

And, the lambda value of the normal rear lambda sensor slowly descends to reach the rich criterion value 1, and after a predetermined time elapses, the lambda value thereof rapidly descends to approach a rich value of 0.92.

Further, the lambda value of a degraded rear lambda sensor descends more slowly to reach to the rich criterion value 1, and after a predetermined time elapses, the lambda value thereof slowly descends to approach a rich value of 0.92.

Referring to FIG. 3, the reaction time of a normal rear lambda sensor is short and the reaction time of a degraded rear lambda sensor is relatively longer than that of the normal rear lambda sensor.

As described above, while the nitrogen oxide purification catalyst 130 is regenerated, the lambda value is detected in real time by the front lambda sensor 110 or the rear lambda sensor 120, such that the degradation thereof can be checked with ease.

In an exemplary embodiment of the present invention, it can be determined that the regeneration of the nitrogen oxide purification catalyst 130 is finished when the lambda value descends after the rear lambda sensor 120 reaches the rich criterion value 1 and a predetermined time elapses.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents. 

1. A degradation rate decision method of a lambda sensor, comprising: an injection step injecting a reducing agent so as to regenerate a nitrogen oxide purification catalyst; a lambda value detection step detecting a lambda value of the lambda sensor from a fuel/air ratio of exhaust gas after injecting the reducing agent; a reaching time decision step determining a time period that the lambda value takes to reach a predetermined criterion value after injecting the reducing agent; and a degradation rate decision step determining that the lambda sensor is degraded when the time period is equal to or longer than a predetermined time period.
 2. The degradation rate decision method of claim 1, wherein the predetermined criterion value is selected from stored map data.
 3. A degradation rate decision system of a lambda sensor, comprising: a nitrogen oxide purification catalyst trapping nitrogen oxide included in exhaust gas flowing in an exhaust line; the lambda sensor mounted on the exhaust line to detect a lambda value as a concentration of a reducing agent included in the exhaust gas; an injector that is mounted at an upstream side of the nitrogen oxide purification catalyst to inject the reducing agent; and a control portion detecting regeneration timing of the nitrogen oxide purification catalyst and controlling the injector to inject the reducing agent, wherein the control portion includes a set of instructions to perform the method of claim
 1. 4. The degradation rate decision system of claim 3, wherein the lambda sensor includes a front lambda sensor disposed at an upstream side of the nitrogen oxide purification catalyst, and a rear lambda sensor disposed at a downstream side of the nitrogen oxide purification catalyst.
 5. The degradation rate decision system of claim 4, wherein the injector injects fuel at an upstream side of the front lambda sensor.
 6. The degradation rate decision system of claim 4, wherein the control portion firstly detects degradation rate of the front lambda sensor, and secondly detects degradation rate of the rear lambda sensor.
 7. The degradation rate decision system of claim 6, wherein the control portion determines that the regeneration of the nitrogen oxide purification catalyst is finished at a dropping time of the lambda value, after the lambda value of the rear lambda sensor reaches a predetermined criterion value in a predetermined time period measured from a time that the reducing agent is injected.
 8. A degradation rate decision system of a lambda sensor, comprising: a nitrogen oxide purification catalyst trapping nitrogen oxide included in exhaust gas flowing in an exhaust line; a lambda sensor mounted on the exhaust line to detect a lambda value as a air fuel ratio included in the exhaust gas; a control portion detecting regeneration timing of the nitrogen oxide purification catalyst and making a reducing atmosphere of the exhaust gas by a post injection of a fuel, wherein the control portion includes a set of instructions to perform the method of claim
 1. 